An electric power steering system generally determines an assist force based upon a steering torque detected by a torque sensor and controls driving of an electric motor.
As an abnormality detection device of a conventional torque sensor, for example, there is the art described in Patent Document 1. In the art, the torque sensor is provided with an abnormality determination unit and a switch unit which turns off when the abnormality determination unit determines there is an abnormality so that an abnormality detection signal is sent from the torque sensor to the ECU through a harness. In this situation, as the abnormality detection signal, a voltage signal which exhibits an L potential when normal and which exhibits an H potential when abnormal is used.